1. Field of the Invention
The present invention relates to a monoclonal antibody or an antibody fragment thereof, which binds to the extracellular region of T-cell immunoglobulin and mucin domain containing molecule-3 (hereinafter referred to as “TIM-3”) and exhibits antibody-dependent cellular cytotoxicity (hereinafter referred to as “ADCC”); a hybridoma which produces the antibody; a DNA which encodes the antibody; a vector which comprises the DNA; a transformant obtained by transforming the vector; a process for producing an antibody or an antibody fragment thereof using the hybridoma or the transformant; and a diagnostic agent or a therapeutic agent using the antibody or the antibody fragment thereof.
2. Brief Description of the Background Art
TIM-3 gene family consists of eight genes in mouse and three genes in human, and each of these genes are located at chromosome 11 and at chromosome 5q33 respectively (Non-patent Document 1). These gene regions are known to be related with autoimmune diseases and allergic diseases. TIM protein is a type I transmembrane protein having a structurally conserved immunoglobulin variable (IgV) domain and a mucin domain.
TIM protein was considered to be specifically expressed on T cells and directly regulate the T cell activity, but there are recent reports on expression of TIM-3 protein in antigen-presenting cells and on their functions (Non-patent Document 2). According to the crystal structure analysis, the TIM protein has a conserved protein structure and has a ligand binding site in the IgV domain.
TIM-3 was identified as a molecule specifically expressed on mouse Th1 cells but not on Th2 cells (Non-patent Document 3). The DNA sequence, the amino acid sequence and the three-dimensional structure of TIM-3 is available in the public data base such as the GenBank accession number NM_032782 and NM_134250. TIM-3 is also known as HAVCR2.
In humans, as similar to mice, TIM-3 is expressed on T-cells as well as phagocytic cells such as macrophages and dendritic cells. Binding of TIM-3 to a protein ligand (e.g., galectin-9) can inhibit the Th1 response via mechanism of apoptosis induction, and therefore lead to such as induction of peripheral tolerance.
The reduction in expression of human TIM-3 with siRNA or the inhibition of human TIM-3 by blocking-antibody increased the secretion of interferon γ (IFN-γ) from CD4 positive T-cells, supporting the inhibitory role of TIM-3 in human T cells. In phagocytes, TIM-3 also functions as a receptor for recognizing the apoptosis cells.
Analysis of clinical samples from autoimmune disease patients showed no expression of TIM-3 in CD4 positive cells. In particular, in T cell clones derived from the cerebrospinal fluid of patients with multiple sclerosis, the expression level of TIM-3 was lower and the secretion level of IFN-γ was higher than those of clones derived from normal healthy persons (Non-patent Document 4). There are reports on relation of TIM-3 with allergic diseases or asthma (Patent Documents 1 and 2).
According to the microarray analysis of hematopoietic stem cells from acute myeloid leukemia (hereinafter referred to as “AML”) patients and normal hematopoietic stem cells, TIM-3 is expressed on AML stem cells and therefore the analysis suggested involvement of TIM-3 in hematological malignancy (Non-patent Document 5 and Patent Document 3).
Examples of the anti-TIM-3 monoclonal antibodies which were established up to now include anti-human TIM-3 rat monoclonal antibody (Clone 344823, manufactured by R&D Systems) and anti-human TIM-3 mouse monoclonal antibody (Clone F38-2E2, manufactured by R&D Systems).